After calling just four witnesses, the defense in the Boston Marathon bombing trial rested its case on Tuesday, clearing the way for closing arguments to be held next Monday, April 6. Closing statements will be followed by the second phase of the trial — the penalty phase — if defendant Dzhokhar Tsarnaev is convicted.

Federal prosecutors rested their case on Monday after bringing 92 witnesses to the stand over 15 days. The prosecution called its final witnesses to describe the bombing victims’ injuries in graphic detail, which left several jurors in tears.

The last witness to testify for the government was the Massachusetts chief medical examiner, Henry Nields, who for 30 minutes described Martin Richards’s various wounds and presented his autopsy photos to the jurors. Richards, 8, was the youngest of the three people to die in the bombings.

According to Nields, Richards quickly bled to death after the largest artery in his body, the aorta, was cut through. His left forearm was almost completely severed, and his spinal cord was cut by a large piece of metal that exited through his back. Many of his internal organs were severely lacerated or ruptured, and he was eviscerated through a large hole in his left abdomen.

For many jurors, the photos were too much. Several cried, and others held their faces in their hands, as Nields gave his graphic report in a steady tone. Nields said he had performed 4,700 autopsies over the course of his career.

Richard was just 53 inches tall and just under 70 pounds when he was brought in for autopsy. He and his two siblings, Jane and Henry, had attended the marathon with their parents, Bill and Denise. His sister Jane lost a leg, while his mother was blinded in one eye. Richard was an athlete and an avid sports fan — he was wearing a New England Patriots t-shirt and a green Boston Celtics shirt when he was killed.

Monday morning began with testimony from another medical examiner who had performed Lingzi Lu’s autopsy. Lu, a graduate student in statistics at Boston University, was killed by the second bomb to go off at the marathon. The prosecution maintains that the second bomb was set off by Tsarnaev, which the defense does not dispute.

The medical examiner described the fatal leg injuries Lu suffered from the blast. She had multiple gaping lacerations on each leg — the two largest were on her upper thigh, six and seven inches long. Her most serious injury was to her left femoral artery, which was completely cut through. The examiner stated the damage would have caused her to bleed to death “within seconds to minutes,” and said that when she examined Lu’s injuries she found round pellets, small nails, and pieces of silver metal from the bomb.

Lu, who was from the city of Shenyang in northeastern China, had a passion for music. Her aunt said she was “a dreamer” and “wanted to do something big,” according to the Boston Globe. Her parents have established The Lingzi Foundation to provide similarly ambitious students with scholarships.

Last Thursday, jurors saw the autopsy photos of Krystal Marie Campbell, who also died from blast injuries to the lower extremities, as well as to the torso. Her left femur broke completely and pellets were found in her skin, along with an embedded piece of metal in the back of her leg. The explosion left her hair singed and her back burned.

Campbell had attended the marathon every year as a spectator. “She had tremendous passion and energy, and Krystle attacked life with vigor and excitement,” Hordon Health, a Boston gym where Campbell had once worked as a fitness coach, said in a statement.

The defense did not cross-examine any of the doctors who testified on the autopsies. Tsarnaev’s attorneys have instead focused on the more technical aspects of the case, including whether Tsarnaev was living with his brother at the time of the explosions, to downplay his role in the preparations.

Once the prosecution finished, the defense began its case by calling FBI photographer Michelle Gamble to the stand, followed by two computer forensics experts and an FBI fingerprint examiner.

If the trial enters the penalty phase, the defense will likely try to demonstrate to jurors how Dzhokhar Tsarnaev was influenced by his brother, Tamerlan. Since a death sentence must be decided upon unanimously, it would take just one juror to keep Dzhokhar off death row.

Renae Reints, a student at Suffolk University, contributed reporting for this article.